Energy associated with an optical signal may be spatially distributed as the optical signal propagates through a waveguide. Different distributions of such optical energy are often referred to as “modes”. In a fundamental mode, the optical energy has a Gaussian distribution, whereby the optical energy is concentrated in the center of the waveguide and tapers off toward the edges of the waveguide. Higher order modes, such as second, third, etc. modes are associated with different spatial distributions of the optical energy.
Optical signals having multiple modes can simultaneously propagate in a waveguide. Conventionally, such multimode signals are generated by passing an optical signal having a signal mode or fundamental mode through a grating. The grating is specifically manufactured such that certain predefined modes are created in the waveguide as the initial optical signal passes through the grating. However, these gratings need to be precisely manufactured to tight tolerances. Otherwise, an optical signal with the desired modes will not be produced. For example, if the grating spacing is note precisely maintained, when the optical signal passes through the grating, undesired modes may be created. Additionally, such fabrication induced errors may result in power loss due to scattering.
Accordingly, an improved system of combining multiple modes of an optical signal is desirable.